1. Field of the Invention
The present invention relates generally to a processing method for repairing a solid body such as an airfoil from a gas turbine engine having a damaged section, and, more particularly, to a method of repairing a portion of the airfoil encompassing the damaged section and utilizing laser shock peening to process a weld joint formed between the airfoil and a replacement piece.
2. Description of the Related Art
Gas turbine engine components such as air foils, rotors and disks are regularly exposed to very high temperatures, vibrations, foreign object damage (FOD) and significant pressure fields as part of the normal operating mode of an engine. These operating conditions typically act over time to deteriorate and weaken the components to make them more susceptible to the formation of damage areas such as pits, cavities, depressions, and cracks. If the damage is not promptly addressed and suitably repaired, the components may become irreparably damaged due to the rapid propagation of existing damage and the reappearance of damage within malrepaired areas. Such irreparable damage becomes more likely to occur within the typical operating environment due to the presence of high cycle fatigue at high temperatures, which serves to accelerate whatever damage already exists within the engine. For the metallic components contained within the engine, the extreme thermal cycling that characterizes normal engine operation represents one of the more deleterious conditions that further aggravates the already severe circumstances under which the components must operate. It is therefore imperative that repair strategies be developed to facilitate a renewal of the engine component that restores it to a physical condition resembling as near as possible its original state. Any repair procedure must not diminish or otherwise adversely effect the functionality and range of operation of the engine component.
Various conventional repair techniques have been developed that aim to fix the damage which appears, for example, within the vane assembly of a gas turbine engine. These approaches have typically focused upon two common types of damage, namely cracks and other such fissures in the edges and sides of the airfoil and voids or other such cavity-like depressions in the major surfaces of the airfoil. Repairing damage to the trailing edge of an airfoil, for example, involves applying a series of weld bead layers of a suitable fill material into the missing edge space to progressively build up the edge until the space is eventually closed out. The fill material is typically built up past the dimensions of the original surface to ensure a proper amount of material accumulation, requiring a deburring process to grind away the excess fill material until the edge conforms substantially to the original surface contour. This procedure clearly features a customized repair operation that tailors the deposition of fill material and the grinding of the excess material to the particular damage under consideration.
Interior surface damage typically takes the form of a cavity or void that arises, for example, when a foreign object such as debris impacts the airfoil surface and causes a portion to break away from or substantially deform the airfoil. In a manner similar to edge build-up, the surface void is filled with a suitable repair material that preferably extends past the surface plane. The excess material is removed by a suitable grinding action until the exposed surface of the fill body is made flush with the adjoining airfoil surface.
These conventional approaches, however, have numerous drawbacks in terms of their applicability to integrally bladed rotors and airfoils in general; effectiveness in repairing wide-scale major damage; ability to treat and counteract the full scope of damage; and suitability within manufacturing and servicing environments that require reproducible standardized repair procedures.
Repair techniques that rely upon resupplying the damage-affected area with fill material to replace the missing airfoil section adopt a customized type of repair strategy that needs to be individually adapted during each repair job to the current damage situation being examined. This customization means that the repair procedure for each damage site will be accompanied by a damage-specific material application sequence to build up the void, followed by a corresponding grinding activity to remove the excess fill material. Performing repairs in this manner prevents the development of a reproducible and repeatable repair procedure characterized by a uniform and universally applicable set of standardized repair steps that do not depend upon the particular form of damage--to the degree evidenced by conventional approaches--in implementing the actual sequence of repair operations.
Another limitation of conventional repair approaches is that only the exposed damage accessible to these repair techniques can be treated. Consequently, some latent deformities may remain within the engine component.
For example, when foreign object damage occurs to the airfoil, the resulting void is clearly apparent and therefore serves as the focus of the repair procedure. However, the impact may also leave residual cracks and other weaknesses in the region of the airfoil surrounding the void that will not be treated by a conventional approach simply involving the application of a fill material and the removal of excess material after build-up. If these residual cracks or other weaknesses are not properly treated, the residual cracks and other weaknesses may form the genesis of further engine component failure. When the engine component is placed back into service without treating potential failure zones such as cracks and areas of weakness (e.g. stress riser), these weaknesses may eventually manifest themselves in a more severe manner as the airfoil is returned to normal operation.
Current repair techniques are generally suitable for handling occurrences of minor damage such as small cracks and pits typically resulting from fatigue and gradual deterioration caused by small FOD. However, these approaches become less desirable and more unsuitable as the damage becomes more aggressive and occupies a greater spatial area. In these situations, the conventional strategy involves replacing the entire engine component (e.g. the entire fan blade comprising an airfoil, base, and root) rather than patching the damaged area.
In an integrated assembly such as an integrally bladed rotor (IBR), there is no opportunity for removal of an individually affected blade because the arrangement of blades is permanently integrated into the rotor. Consequently, conventional approaches are completely unsuited for repairing IBRs, to the extent that such approaches recommend replacement of an individual blade as a feature of the repair solution. Additionally, as noted above, it is customary in conventional approaches to remove the affected blade and deliver it to a repair site even in the event of damage that does not necessitate the replacement of an entire engine component. This aspect of implementation suggests for conventional repair procedures a degree of incompatibility with respect to handling IBRs or any other integrated component configuration that does not permit or make feasible the removal and reattachment of some portion, such as an airfoil.
Two patents which are directed to gas turbine engine vane repair are U.S. Pat. Nos. 5,584,662 and 5,675,892, entitled "LASER SHOCK PEENING FOR GAS TURBINE ENGINE VANE REPAIR". Both utilize the technique of braze filling a void formed in a damaged vane followed by laser shock peening the surface of the brazed filled void.
An additional method of gas turbine engine repair is disclosed in U.S. Pat. No. 5,735,044 entitled "LASER SHOCK PEENING FOR GAS TURBINE ENGINE WELD REPAIR". This patent is directed to repairing an engine component by first laser shock peening the surface of an engine component around a damaged portion to impart deep compressive residual stresses extending into a substrate bond surface of the engine component. Following laser shock peening a metallic filler is bonded onto the substrate.